WASHINGTON—The U.S. is pushing to expand a secret CIA effort to help Pakistan target militants in their havens near the Afghan border, according to senior officials, as the White House seeks new ways to prod Islamabad into more aggressive action against groups allied with al Qaeda,

The push comes as relations between Washington and Islamabad have soured over U.S. impatience with the slow pace of Pakistani strikes against militants who routinely attack U.S.-led troops in Afghanistan. President Barack Obama has said he will begin to withdraw troops from Afghanistan in July, increasing the urgency to show progress in the nine-year war against the Taliban.

The U.S. asked Pakistan in recent weeks to allow additional Central Intelligence Agency officers and special operations military trainers to enter the country as part of Washington's efforts to intensify pressure on militants.

The requests have so far been rebuffed by Islamabad, which remains extremely wary of allowing a larger U.S. ground presence in Pakistan, illustrating the precarious nature of relations between Washington and its wartime ally.

The number of CIA personnel in Pakistan has grown substantially in recent years. The exact number is highly classified. The push for more forces reflects, in part, the increased need for intelligence to support the CIA drone program that has killed hundreds of militants with missile strikes. The additional officers could help Pakistani forces reach targets drones can't.

There are currently about 900 U.S. military personnel in Pakistan, 600 of which are providing flood relief and 150 of which are assigned to the training mission.

A senior Pakistani official said relations with the CIA remain strong but Islamabad continues to oppose a large increase in the number of American personnel on the ground.

The Obama administration has been ramping up pressure on Islamabad in recent weeks to attack militants after months of publicly praising Pakistani efforts. The CIA has intensified drone strikes in Pakistan, and the military in Afghanistan has carried out cross-border helicopter raids, underlining U.S. doubts Islamabad can be relied upon to be more aggressive. Officials have even said they were going to stop asking for Pakistani help with the U.S.'s most difficult adversary in the region, the North Waziristan-based Haqqani network, because it was unproductive.

The various moves reflect a growing belief that the Pakistani safe havens are a bigger threat to Afghan stability than previously thought.

When senior Pakistani officials visited Washington this week, Obama administration officials signaled they are willing to push for a long-term military aid package. But they also have made clear to Pakistani officials they expect tangible results, and they threatened that current cash payments to Pakistan could be reduced if things don't improve in tribal areas such as North Waziristan.

The current efforts to expand CIA presence are meant to expand intelligence collection and facilitate more aggressive Pakistani-led actions on the ground. Some U.S. officials, however, remain hopeful that Islamabad will allow a greater covert presence that could include CIA paramilitary forces.

Given Pakistan's objections to U.S. ground troops, using more CIA paramilitary forces could be a "viable option," said a government official. "That gives them a little bit of cover," the official added, referring to the Pakistanis.

U.S. officials said a stronger U.S-Pakistan intelligence partnership would not be a substitute for closer working relationship with the military's special operation forces.

Much of the on-ground intelligence in Pakistan is gathered by the country's Inter-Services Intelligence agency. Some U.S. officials believe Pakistan wants the U.S. to remain dependent on the ISI for that intelligence.

While the Obama administration has been focused on North Waziristan, officials said there also is a need for Pakistani operations in the southern city of Quetta and the surrounding province of Baluchistan. The U.S. hopes that if it can develop precise information on militant leaders, it could entice the Pakistan government to arrest some top members of the Quetta Shura, the ruling council of the Afghan Taliban movement.

Some officials are hopeful that Islamabad will reverse course and grant the additional CIA and military visas in the coming days. The Pakistani government has in the past used its control over visas to express displeasure with U.S. policy and limit the number of Americans who can work in the country.

Tensions remain between the Pakistan military and the U.S. military in Afghanistan, especially after a series of cross border raids by NATO in recent weeks.

In September, the CIA stepped up the pace of drone strikes in Pakistan, in part to counter suspected terrorism plots in western Europe as well as cross-border attacks by the Haqqani network. The stepped-up activity by the CIA has received little criticism from Pakistan, and tacit support from the government.

CIA Director Leon Panetta, who visited Islamabad late last month, said ISI has been "very cooperative," playing down tensions over U.S. allegations that elements of the intelligence agency were helping the Haqqanis and other militant groups fighting the U.S. "We're getting good cooperation," Mr. Panetta said.

Pakistani officials believe the CIA is better able to keep details of its operations largely out of the public eye, although the agency's drone program has received widespread attention and is enormously unpopular with the Pakistani public.

U.S. military forces on the ground remain a red line for Islamabad. A senior Pakistani official said if the Pakistan public became aware of U.S. military forces conducting combat operations on Pakistani territory, it would wipe out popular support for fighting the militants in the tribal areas. Whether covert CIA forces would cross that line however, remains an open question.

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